1. Field of the Invention
This invention relates to a waste melting furnace proposed to reduce fuel consumption and prevent scattering of dust produced when a waste such as sludge is blown in powder form into a filling layer of a carbon type combustible such as coke to burn the waste and melt the waste into slag. More particularly, the invention relates to a waste melting furnace having a filling layer formed of a carbon type combustible, and an annular combustion space formed around the filling layer below an upper surface thereof and communicating with the filling layer. A waste is supplied in powder form into the combustion space, whereby the waste is burned and slagged in the combustion space and filling layer.
2. Description of the Related Art
When a waste such as sludge is blown in powder form directly into the filling layer in a hot hearth to burn and melt the waste, the waste (sludge) tends to adhere to surfaces of coke to hamper combustion. The temperature of the filling layer also is lowered by an endothermic phenomenon or the like due to the decomposition of organic substances. As a result, the furnace becomes increasingly choked by dust, thereby deteriorating the efficiency of operation.
To eliminate the above drawbacks, a method of burning and melting a waste has been proposed in Japanese Patent Application No. 2-131746, for example. According to this method, as shown in FIG. 2(b), a combustion space is formed manually around a filling layer, and combustion gas is fed from the combustion space sideways toward the filling layer.
In this construction, the powdery waste blown in and burned in the combustion space should be melted, charred and slagged in the coke layer to be discharged through an outlet. In practice, however, the waste often becomes scattered as dust into exhaust gas instead of being trapped by the coke layer. Further, in the above burning and melting structure, large quantities of peripheral flows occur in the filling layer so that only regions adjacent peripheral walls become hot. This is considered due to a "peripheral fluidization phenomenon" occurring with an ordinary filling layer structure. That is, in the filling layer structure, the gas blown in through a tuyere tends to flow more smoothly adjacent the peripheral walls than in central regions of the furnace. In a steel making blast furnace, for example, gas velocities in peripheral regions are said to be at least twice gas velocities in central regions. This phenomenon is outstanding where, as in the present invention, a thin filling layer structure is employed.
Thus, the powdery waste blown in is considered to pass through the peripheral walls to scatter in the exhaust gas. Since the gas flows in reduced quantities toward the center of the furnace, the temperature in the furnace center does not become sufficiently high. The furnace inevitably has an uneven temperature distribution therein.
Consequently, the above waste melting furnace tends to suffer the following disadvantages:
(1) Scattering of dust (short-path of the powdery waste), PA1 (2) Bridge formation in the filling layer due to the uneven distribution of temperature in the furnace, PA1 (3) Increase in coke consumption due to partial combustion of peripheral coke portions and scattering of unburned powdery waste, and PA1 (4) Defective output due to an unstable operation of the furnace.